Self-organized nanostructures forming under high-repetition rate femtosecond laser bulk-heating of fused silica.

Abstract

Femtosecond laser exposure of fused silica can lead to non-linear absorption, eventually causing structural modifications in the material. Above a given pulse repetition frequency, the effects from one pulse to the next one become cumulative leading to a localized bulk heating of the substrate, and in turn, to the dissociation of the glass matrix leading to gas bubbles formation. Here, we investigate the dynamics of bubbles formation as a function of the incoming net fluence. In particular, we observe evidences of laser trapping of gas bubbles and the unexpected formation of self-organized nanostructures, resembling nanogratings normally found at much lower repetition rate, i.e. when cumulative effects are absent.